The present invention concerns a dewatering element on the forming section of a paper or board machine, where the forming section comprises a movable wire, which is in contact with the wall of the dewatering element, with the wall having a non-pulsating suction zone which is at least as wide as the wire. The present invention also concerns a cover of a dewatering element of a paper or board machine.
Pulsating and non-pulsating dewatering elements have been used on paper and board machines. Non-pulsating dewatering elements provide good retention. Pulsating dewatering elements, in turn, give good formation. Non-pulsating dewatering is often arranged by means of a roll unit followed by a pulsating foil unit. This arrangement first provides good retention and then improved formation. The use of a roll gap former imposes restrictions on the speed applied. Blade gap formers, which feature pulsating dewatering right at the beginning, have hence been introduced in order to enable increased speed. However, retention has been very low with these, and the paper is anisotropic in the z direction. Problems encountered in the above-mentioned technologies have been solved for example through means described in patent publication WO2004/018768. In the technology presented in this publication, non-pulsating dewatering elements have been implemented by means of a non-pulsating suction zone included in the dewatering element. It is well known that retention is better with this type of non-pulsating dewatering than with pulsating dewatering, but formation is poorer. Furthermore, the dimensions of the paper or board machine grow as the machine speed increases.